01 - Pulse flour, powdered sugar, and salt in a food processor. Add cold butter and pulse until mixture resembles coarse crumbs. Add egg yolk and pulse again. Drizzle in cold water, 1 tablespoon at a time, until dough just comes together.
02 - Turn dough onto a floured surface, shape into a disk, wrap in plastic, and refrigerate for at least 1 hour. Preheat oven to 350°F. Roll dough to fit a 9-inch tart pan. Press into pan and trim excess. Prick base with a fork.
03 - Line tart shell with parchment and fill with pie weights or dried beans. Bake for 15 minutes. Remove weights and parchment; bake 10 more minutes until golden brown. Cool completely before filling.
04 - Heat milk and vanilla bean (or extract) in a saucepan until just simmering. Remove from heat. Whisk egg yolks, sugar, and cornstarch in a bowl until smooth.
05 - Gradually whisk hot milk into egg mixture. Return to saucepan and cook over medium heat, whisking constantly, until thickened and bubbling for 2-3 minutes. Remove from heat and stir in butter until smooth.
06 - Transfer custard to a bowl, cover with plastic wrap touching the surface to prevent skin formation, and refrigerate until completely cool, at least 1 hour.
07 - Spread cooled custard evenly in baked tart shell. Arrange fresh fruit decoratively over the custard in your desired pattern.
08 - Warm apricot jam with water in a small saucepan until melted and smooth. Strain if necessary. Brush glaze gently over fruit using a pastry brush to create a shiny finish.
09 - Refrigerate assembled tart for 1 hour before serving to allow flavors to meld and custard to set properly.